Received for publication May 9, 2008.
Revised June 20, 2008.
Accepted for publication June 23, 2008.

Local not systemic modulation of dendritic cell S1P receptors in lung blunts virus-specific immune responses to influenza

Abstract

The mechanism by which locally delivered sphingosine analogs regulate host response to localized viral infection has never been addressed. In this report, we show that intra-tracheal (i.t.) delivery of chiral sphingosine analog AAL-R or its phosphate ester inhibits the T cell response to influenza-virus infection. In contrast, neither intra-peritoneal (i.p.) delivery of AAL-R nor i.t. instillation of the non-phosphorylable stereoisomer AAL-S suppressed virus-specific T cell response, indicating that in vivo phosphorylation of AAL-R and S1P receptor modulation in lungs are essential for immunomodulation. I.t. delivery of water soluble S1P₁ receptor agonist at doses sufficient to induce systemic lymphopenia did not inhibit virus-specific T cell response indicating that S1P₁ is not involved in the immunosuppressive activities of AAL-R and that immunosuppression acts independently of naive lymphocyte recirculation. Accumulation of dendritic cells (DCs) in draining lymph nodes was inhibited by i.t. but not i.p. delivery of AAL-R. Direct modulation of DCs is demonstrated by the impaired ability of virus-infected bone-marrow derived DCs treated in vitro with AAL-R to trigger in vivo T cell response after adoptive transfer to the airways. Thus, our results suggest that locally delivered sphingosine analogs induce immunosuppression by modulating S1P receptors other than S1P₁ or S1P₂ on dendritic cells in the lungs after influenza virus infection.

Key words: Gi family, Sphingolipids, Leukocytes/Mast cells